A finite element model of ferroelastic polycrystals

A finite element model of switching in polycrystalline ferroelastic ceramics is developed. It is assumed that a crystallite switches if the reduction in mechanically driven potential energy of the system exceeds a critical value per unit volume of switching material. Stress induced (i.e. ferroelastic) switching is a change of permanent strain in characteristic crystallographic directions. Martensitic twinning is one example, but the strain response of ferroelectric materials has the same characteristics. The model is suitable for representing ferroelastic systems such as shape memory alloys and as a preliminary model for ferroelectric/ferroelastic materials such as perovskite piezoelectrics. In the simulations, each crystallite is represented by a finite element and the crystallographic principal direction for each crystallite is assigned randomly. Different critical values for the energy barrier to switching are selected to simulate stress vs strain hysteresis loops of a ceramic lead lanthanum zirconate titanate (PLZT) at room temperature. The measured stress versus strain curves of polycrystalline ceramics designated PZT-A and PZT-B are also reproduced by the model. (C) 1998 Elsevier Science Ltd. All rights reserved.